Typically, fires involve a chemical reaction between oxygen and a fuel which is raised to its ignition temperature by heat. In general, suppression or extinguishment of fires has involved one or more of the following procedures: removing the oxygen, reducing the temperature in the environment of the fire, physically separating the oxygen from the fuel and/or interruption of the chemical reactions of the components. A number of means of accomplishing the foregoing methods are known. Physical agents operate primarily on heat absorption and chemical agents operate primarily by removing free radicals from the flames and the combustion system. Among the agents employed there may be mentioned water, carbon dioxide, dry chemicals and Halon halocarbons.
Although Halon halocarbons have been used extensively in the past, there is a need to eliminate their use due to the harmful effects they are considered to have on the environment, particularly their zone depleting aspect with respect to the atmosphere.
Due to the necessity for large cylinders to contain a very limited amount of carbon dioxide gas, use of carbon dioxide has been very restricted.
Probably the most commonly used fire suppressing material has been water. Heretofore, water-based indoor fire suppression has generally been in the form of water sprinkler systems which generally operate at ordinary building or municipal water pressure. These systems depend upon distributing a plurality of sprinkler heads around an area to be protected. Such systems can be relatively complex and expensive, requiring piping interconnecting the sprinkler heads and running to a suitable source of water, which is normally at the pressure provided in the facility or building, or the municipal or other provider of water pressure, that is, a relatively low pressure.
A more recently emerging technology in fire protection is to use some form of water mist system. Such systems use relatively small amounts of water in the form of a fine mist to extinguish a fire rather than the relatively large volume of water that an ordinary sprinkler system would typically distribute or apply. A water mist operates to extinguish a fire by at least two different mechanisms, namely, by extracting heat and by displacing oxygen. Such systems use relatively small amounts of water in the form of a fine mist of very small (e.g. 50 microns) water droplets to extinguish fires.
The vaporization of water to steam is very effective in removing heat from the fire. Again, however, one of the drawback to the use of water is the limited amount of water that can be conveniently stored for use in fire suppression systems. A further drawback has been the necessity, in some situations, to provide expensive means for converting the stored water to water vapor for use in suppressing a fire by oxygen displacement.